This invention relates to double-acting jacks of the type which have positive stops and, more particularly, to such jacks having positive stops which are adjustable.
The invention concerns an improvement hydraulic or pneumatic double-acting jacks equipped with adjustable, positive stops, notably of the type described in French Pat. No. 1,128,138. This French patent discloses a double-acting jack associated with an adjustable, positive stop which determines the length of the stroke, and against which the piston can abut. The stop is constituted by a nonrotatable nut, the nut being axially displaceable, by manipulation of a lead screw which is axially immobilized, with which it is in mesh. The lead screw is capable of being set in rotation for the purpose of adjusting the position of the nut.
This type of jack has the advantage of allowing considerable precision in determining the final end-of-stroke position of the piston rod.
However, it is necessary for the lead screw to be able to support the thrust developed by the piston, which, in the case of high-powered jacks, requires the designer to design the jacks to be of considerable size and have components of large dimensions. These known jacks consequently are expensive and cumbersome. Therefore, for a given piston diameter, a specific thrust must not be exceeded, otherwise, the mechanical stresses will exceed the tolerance values for correct fatigue resistance of the adjustable stop and the screw which supports it, as well as additional components, such as the stop ring, holding screw, and others.